1. Field of the Invention
The present invention is related to the field of network telephony, and more specifically to devices, softwares and methods for improving a quality of a telephone call performed via a network.
2. Description of the Related Art
Packet switched networks, such as the internet, are increasingly used for voice communications. These communications are implemented using telephone devices that are connected to special network devices called gateways. The voice data is typically exchanged under a special protocol called Voice over Internet Protocol (VoIP). Sometimes the telephones are IP (Internet Protocol) telephones, and the gateways are voice gateways.
The telephone devices sometimes have an acoustic echo canceller. This feature minimizes how much echo of a voice communication is returned to the other party.
Acoustic echo cancellers typically adapt to the acoustic characteristics of the room. They tend to work intensively during the beginning of a voice communication, and often during it.
A problem with adaptive acoustic echo cancellers occurs during and immediately after call setup, when an acoustic echo canceller works the most intensively. Call progress tones are heard which include DTMF (Dual Tone Multi Frequency) tones, and are given disproportionate weight. Adaptive acoustic echo cancellers adapt particularly well to those, because of their periodicity.
Such adapting generates problems, because later other tones might be canceled out, by being treated as echoes. Such other tones include those, for example, of call waiting. In addition other sounds present during typical call set up (paper shuffling, finger tapping) tend to cause tones to fade in and out, especially in speakerphone applications. Fading in and out tends to be very annoying.